Various methods are known and have been proposed to control the flow of liquid from a source and the present invention is particularly concerned to provide a method and means for controlling the flow of liquid from a body of the liquid and in particular the flow of water from dams, water storage systems and other bodies of water.
When large volumes of water are stored the rapid discharge of water from the storage medium can create problems, particularly if it is intended to discharge water at or near the level of the head of the water. If water is to be discharged over or through a discharge outlet that is adjacent to the normal level of water within the storage medium, then a significant weight of water must be built up in the storage medium above the level of the outlet before the water will flow freely. This can have a detrimental effect not only on the storage medium, but also on the environment downstream of the discharge point because with known technology it is not possible to adequately regulate the flow of water under low head conditions. It is considered that there are considerable advantages in facilitating the discharge of water over or through an outlet at a rate which is greater than the rate that would normally be generated by the head of water behind the outlet.
When electric power is generated through a hydro electrical system, the energy to rotate the electrical generators is generally obtained by leading water from a dam through a penstock or other usual form of closed or open race to the generator. Generally therefore the generators are situate considerably below the level of the head of the water. Because of the high energy requirements of the electrical power generation systems, very large volumes of water are required which results in the construction of massive dams to store the water. The ecological disadvantages of such dams are significant, not only because of the large tracts of land that must be flooded to provide the head of water, but also in the construction of the dam and the interruption of the flow of water that would have otherwise been available for other purposes.
It is apparent that a system that would enable comparable electrical power to be generated by using less head of water than was previously possible would provide considerable advantages not only to the owner of the electricity generating system but also to the surrounding ecology. That would mean the size of the dam and the volume of the body of the water required to be stored behind the dam can be lessened.
It is well known to harness energy from water to drive pelton wheels and other means of transforming the flow of water into a mechanical rotatory motion. In these situations comparatively small dams are often built and the energy transforming means is situated at or adjacent to the foot of a spillway from the dam. It is considered that if the flow of water from the stored water can be enhanced, particularly by increasing the speed of water flowing down the spillway, then less water will be required to generate the same amount of power. This would have considerable advantages where the volume of water is scarce since it would enable smaller storage systems to be built to obtain the required amount of energy.
It is an object of this invention to provide means for enabling liquid to be discharged from a source of the liquid at or about the level of the head of the liquid in a manner that the liquid will flow from the source of liquid at a rate that is faster than if the means were absent.
Accordingly one form of the invention may be said to comprise a liquid flow control device wherein a controller having a leading edge and an essentially planar undersurface is positioned above the entrance to a spillway which communicates with a source of the liquid to provide a gap between the entry to the spillway and the underside of the controller and wherein an angle of attack is formed between the spillway and the undersurface of the controller which will create an accelerative venturi effect on liquid passing through the gap onto the spillway.
Preferably the controller is located above the entrance to the spillway be means which will enable the controller to pivot to cause the angle of attack to change.
Preferably the controller is located above the spillway be means which will enable the gap between the controller and the spillway to be increased or decreased.
Preferably the source of liquid comprises a dam.